1. Field of the Invention
The present invention is generally in the field of electronic circuits and systems. More specifically, the present invention is in the field of electronic communication circuits and systems.
2. Background Art
Wireless receivers, such as those used in Bluetooth, cellular, or WiFi systems, for example, using phase-shift keying (PSK) or frequency-shift keying (FSK), as well as other types of modulation can suffer from degraded demodulation performance and diminished signal reception when DC offset is present or generated in the receiver. Direct conversion receivers are particularly sensitive to DC offset, since a received signal is directly converted down to baseband where the DC offset is imposed.
If the DC offset in a signal can be accurately estimated, then the DC offset can be subtracted to improve performance and signal reception in the receiver. One conventional approach for estimating DC offset in a receiver takes the long term average of the incoming signal and uses that as the DC offset estimate. However, this estimate can be biased by the data content of the incoming signal. If the incoming signal has numerous togglings between zero and one data bits, for example, then the DC offset estimate will be weighted towards such data content, which can be an inaccurate estimate of the DC offset and degrade performance. In another conventional approach, DC offset in a Bluetooth device is estimated by analyzing the preamble of a Bluetooth packet, which contains only a fixed zero-one pattern of four symbols. One problem with this approach is that the preamble comes so early in the Bluetooth packet that the receiver's automatic gain control (AGC) is unlikely to be settled, so subsequent changes to the AGC will impact the DC offset.
Thus there is a need in the art for a method of effectively determining DC offset in AC signals, for example, those received in wireless systems, without the shortcomings of the conventional methods.